1. Field of the Invention
The present invention relates to a sealing technique for preventing the deterioration of an organic EL material due to moisture in an organic EL display device.
2. Description of Related Art
Although a main stream of the conventional display device is a CRT, a liquid crystal display device, a plasma display device and the like which are flat display devices have been practically used in place of the CRT and a demand for such flat display devices is increasing. In addition to these display devices, developments and efforts for practical use of a display device which uses organic electro luminescence (hereinafter, referred to as organic EL display device) and a display device which arranges electron sources utilizing field emission in a matrix array and phosphors arranged on an anode is radiated with light thus forming an image (hereinafter referred to as FED display device) have been also in progress.
The organic EL display device has features such as (1) the organic EL display device is of a self-luminous type compared with liquid crystal and hence, a backlight is unnecessary, (2) voltage necessary for emission of light is low, that is, equal to or below 10V and hence, the power consumption can be decreased, (3) compared to a plasma display device or an FED display device, the vacuum structure is unnecessary thus the organic EL display device is suitable for achieving the reduction of weight and the reduction of thickness, (4) a response time is short, that is, several micro seconds and hence, the organic EL display device exhibits the excellent motion picture property, and (5) the viewing angle is 170 degrees or more.
However, when moisture or oxygen is present around the EL material, the oxidation of the EL material is accelerated thus generating dark spots whereby the light transmitting property is deteriorated. To cope with such a drawback, there has been adopted a method in which, after formation of lines, switching elements, organic EL layers and the like on a substrate, a glass substrate or a sealing cap for sealing is mounted on a back surface of the substrate to form a sealed space, and a desiccant is arranged in the inside of the sealed space. Due to such a method, it is possible to remove the moisture from the inside of the display device in which the organic EL material is formed.
FIG. 12 is a schematic cross-sectional view showing an example in which lines, switching elements, organic EL layers and the like are sealed using a sealing can 15. Although an undercoat 2, lines, switching elements and the like are formed on a substrate 1, these parts are omitted from FIG. 12. An organic EL film 11 emits light by applying a voltage between a lower electrode 9 and an upper electrode 12. The sealing can 15 is mounted on the substrate 1 using an adhesive material 16 so as to maintain the inside of a display device in a hermetic state. To remove moisture from the inside of the display device, a desiccant 19 is mounted on the inside of the sealing can 15. The desiccant 19 is fixed to the inside of the sealing can 15 using a pressure-sensitive adhesive double-coated tape 191, for example. As a material of the sealing can 15, for example, metal such as stainless steel can be used. As a material of the desiccant 19, activated carbon, zeolite, silica gel or the like can be used.
FIG. 13 shows an example in which the inside of a display device is hermetically maintained using a back glass plate 17. To ensure a space between the back glass plate 17 and the substrate 1, the back glass plate 17 is mounted on the substrate 1 by way of a sealing frame 18 using a sealing material 16 thus hermetically sealing the inside of the display device. In this case, a desiccant 19 is fixed to the inside of the back glass plate 17 using a pressure-sensitive adhesive double-coated tape 191 or the like. A material of the desiccant 19 may be substantially equal to the desiccant used in the case of the sealing can 15.
The above-mentioned related arts are described in, for example, patent document 1, patent document 2 and the like.
[Patent document 1] JP-A-3-261091
[Patent document 2] JP-A-2001-345175